nixos/gollum: replace deprecated usage of PermissionsStartOnly

see https://github.com/NixOS/nixpkgs/issues/53852

nixos/modules/services/misc/gollum.nix

@@ -75,27 +75,24 @@ in
 
     users.groups.gollum = { };
 
+    systemd.tmpfiles.rules = [
+      "d '${cfg.stateDir}' - ${config.users.users.gollum.name} ${config.users.groups.gollum.name} - -"
+    ];
+
     systemd.services.gollum = {
       description = "Gollum wiki";
       after = [ "network.target" ];
       wantedBy = [ "multi-user.target" ];
       path = [ pkgs.git ];
 
-      preStart = let
-          userName = config.users.users.gollum.name;
-          groupName = config.users.groups.gollum.name;
-        in ''
-        # All of this is safe to be run on an existing repo
-        mkdir -p ${cfg.stateDir}
+      preStart = ''
+        # This is safe to be run on an existing repo
         git init ${cfg.stateDir}
-        chmod 755 ${cfg.stateDir}
-        chown -R ${userName}:${groupName} ${cfg.stateDir}
       '';
 
       serviceConfig = {
         User = config.users.users.gollum.name;
         Group = config.users.groups.gollum.name;
-        PermissionsStartOnly = true;
         ExecStart = ''
           ${pkgs.gollum}/bin/gollum \
             --port ${toString cfg.port} \